Weak cytotoxic T lymphocyte (CTL) responses against the EBV antigens EBNA1, LMP1 and LMP2 have been observed in Hodgkin disease, Burkitt lymphoma and nasopharyngeal cancer, but have been insufficient to eradicate tumor cells. Thus, a broadly effective anti-EBV-tumor immunotherapy, based on MHC class I-restricted peptides, is lacking. The central hypothesis to be tested in Project 2 is that immunogenic MHC class Il-restricted peptides from EBNA1, LMP1 and LMP2 (especially) are present in EBV-positive tumor cells and can be used to improve the priming and activation of CD8+ T cells, leading to more potent antitumor immunity. This prediction will be tested by direct stimulation of human PBMCs with computer-predicted peptides or, alternatively, in HLA-DR or DP transgenic mice deficient in MHC class II molecules (Aim 1), followed by efforts to improve the immunogenicity of the most promising peptides (Aim 2) and then by clinical evaluation in Hodgkin disease and neuroblastoma patients (Aim 3), in collaboration with the leaders of Projects 1 and 3.This combination of strategies is designed to detect the majority of immunogenic MHC class II-restricted peptides (or their variants) with enhanced potency for eliciting T cell responses. With these characterized epitopes in hand, it will be possible to consider novel ways to enhance immune responses against EBV-associated tumors and perhaps against other malignant diseases as well. Frequent interactions with other investigators in the program will be essential to a successful conclusion of this project, and will be particularly evident during years 4 and 5, during clinical evaluation of promising peptide vaccines.